A tray sealer is known from EP 2 141 095 A1, in which a transfer carriage moves along guides in the direction of transport, and a motion of the gripper arms relative to each other is generated by a rotational motion of the guides.
A tray sealer is known from EP 0 334 266, in which two transfer carriages are arranged laterally below a conveyor belt conveying the trays to a sealing station, and gripper arms are moved towards each other for receiving trays using a pivot lever on each transfer carriage on which a gripper arm is mounted.
A tray sealer is known from EP 1 996 470 in which a gripper system with a carriage, a pivot mechanism, and two gripper arms is provided above the transport plane for the trays and a speed difference between the drive of the carriage and a drive for the pivoting mechanism provides for the movement of the gripper arms towards each other.
A common disadvantage of the above-described tray sealers according to prior art is that the gripper arms are moved towards each other not in parallel, and not at a fixed distance from the transport plane for the trays. Depending on the size of the trays, the gripper arms are moved to a different distance towards each other for receiving the trays and thereby have differing heights relative to the transport plane and thus relative to the tray bottom. Due to a collision with the gripper arms and the sealing tool lower part during the closing motion and the resulting vertical motion, it is hardly possible to grip shallow trays. Due to the lateral dimension of the sealing tool lower part and/or the sealing tool upper part and a limited reach of the gripper arms, narrow trays can only be gripped when the sealing tool lower part and/or the sealing tool upper part with smaller lateral dimensions and adapted gripper arms are simultaneously replaced, in order to be able to move the gripper arms closer to each other.
WO 2011/018 391 shows a tray sealer with horizontal gripper arm adjustment at a transfer carriage being arranged above the transport plane, where drives riding along with the transfer carriage are provided for the gripper arm adjustment. Such a tray sealer has the drawback that the swing of the gripper arms is limited by the guides provided horizontally and transversely to the direction of transport, and that the inertial mass of the transfer carriage is large due to the drives riding along for the gripper arm adjustment.